This invention relates to air-conditioning systems and more particularly to a method of, and composition for, reduction in pathogens associated with the filters in such systems. The invention has been developed primarily for use in air-conditioning (including air cooling and air heating) systems, and will be described hereinafter with reference to this field of use. However, it will be appreciated that it is not limited to that particular use
Air conditioning systems such as are commonly provided in office, residential, health care and other buildings incorporate air filters. An example of such a filter employs non-woven polyester fibres as media to filter airborne particulates in excess of about 10 microns in size from the air, but filters are made from a wide variety of materials, in many different constructions and grades. The function of the filter is to trap dust and particulate contaminants. This trapped matter (the xe2x80x9cfiltratexe2x80x9d) provides a haven for the growth of pathogens such as fungi, bacteria, viruses, allergens, yeasts, and moulds. Conditions for the growth of such organisms are especially favourable during periods of high humidity such as may occur when the system is off, for example at night, but also arise during normal operation. The presence of organisms is highly undesirable because they can cause illness or death in humans and animals, create odours and can damage or destroy a wide variety of materials.
Of particular concern in terms of human health and safety are endotoxins and mycotoxins which are breakdown components of fungal and bacterial cell walls and which are known human respiratory allergens. In some individuals they can trigger asthma attacks, and in all cases have been shown to cause immune response. Over a period of exposure this reduces the ability of the immune system to respond to antagonists and leaves the subject more prone to infection by bacteria, viruses, etc. Also of concern are fungal spores, bacterial spores and bacteria.
The prevention of spore germination and microbial survival in air filtration devices would help reduce the risk of illness and hypersensitivity reactions. It would also increase the useful life of the filtration devices. Microbial activity shortens the life of the filter itself because the increase in biomass on and in the filter can clog pores, lessen air-flow and increase back pressure in the system. In some cases, air filters are prepared from or include natural materials such as cellulose and in that case are rapidly degraded under moist conditions by certain fungi.
It is a major concern in health care facilities such as hospitals and nursing homes that dangerous infectious diseases may be spread by a wide variety of micro-organisms. The problem is exacerbated in such facilities because many of the patients are in a weakened condition due to their primary health care problem. Micro-organisms that would not be a major threat to a healthy person can be fatal to a patient with a diminished capacity to defend themselves from infection.
Increasing attention is also being paid to other environments such as public buildings, since if pathogenic microorganisms find their way via conditioned air or ventilation shafts, into a building they can be rapidly circulated throughout the building thereby greatly increasing the likelihood of the spread of infection and disease.
One proposed solution to this problem has been to coat filter materials with a biocidal composition. The biocides have been bound onto or into the filter fibres for example by inclusion within polymers prior to extrusion as filter fibres. The present inventor has discovered that such so-called xe2x80x9cantimicrobialxe2x80x9d filters are biostatically effective when the surface of an unused xe2x80x9cantimicrobialxe2x80x9d filter material is inoculated with bacteria and/or fungal contaminant in the laboratory, but that the filter becomes progressively ineffective with passage of time in actual use in an air-conditioning system. Consequently the filter should be frequently removed for cleaning and retreatment or replaced. Removal is costly and inconvenient in terms of labour required and downtime, as well as being potentially hazardous, while retreatment or replacement is expensive. Typically the filters are only removed when the airflow resistance becomes unacceptable.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
It is an object of the present invention to overcome or ameliorate at least one of the deficiencies of the prior art, or to provide a useful alternative.
Many regions of the world employ heated filtered air in buildings as a means of central heating. It will be understood that the furnace and other filters of such systems contribute to the same hazards as described above for air conditioning filters and the invention is not limited to any particular kind of filter or airflow system. It will also be understood that the invention is equally applicable to filters of different kinds and grades, for example to hepafilters.
According to a first aspect, the invention provides an air filter including a composition, said composition including a biostatic or biocidal agent wherein the agent is adapted to migrate through particulates accumulating in use on the filter.
For preference, the biostatic or biocidal agent is selected to have bacteriostatic and/or fungistatic properties. The particulates usually accumulate in layers and the biostatic or biocidal agent of the invention migrates through the layer to the outside surface (air/particulate interface) where organic matter would otherwise multiply.
In filters according to the invention the biocide is not bound to the filter surface but is adapted to migrate through the accumulating dust and particulate matter on the filter. Particles in the layer become coated with biocide or biostat.
It will be understood that it is sufficient that the treatment is bacteriostatic or fungistatic. That is to say, it is sufficient that the treating agent stops colonisation on the filter rather than hills organisms in a colonised filter. However biocidal compositions may be used.
According to a second aspect, the invention provides a composition for application to an air filter including:
a water soluble biocidal or biostatic agent,
and a humectant
whereby the biocidal or biostatic agent is adapted to migrate through a filtrate accumulating, in use, on a surface of the air filter;
It is highly preferred that the composition further includes a surfactant and desirably a fluorosurfactant.
In highly preferred embodiments the composition includes one or more rheological additives for example a thickening agent, a gelling agent, or a viscosity modifier.
According to a third aspect, the invention provides a method of treating a filtrate on a filter including the step of adding to the filter or to the filtrate a biocidal or biostatic agent adapted to migrate through the filtrate
According to a fourth aspect, the invention provides a method of reducing airborne contaminants in air including the step of:
treating a filter with an agent according to the second aspect,
passing air through the filter whereby to accumulate contaminants as a filtrate on the filter, and
allowing the biocide to migrate into the filtrate.